1. Technical Field
The present invention relates to a method of manufacturing a multi-layered wiring board, to an electronic device, and to an electronic apparatus including a multi-layered wiring board manufactured by the above method.
2. Related Art
Conventionally, a method of manufacturing a multi-layered printed wiring board includes a method implemented by the following processes.
A single-layer substrate on which a pattern is formed by etching is positioned, and then respective layers are laminated thereon. In order to electrically connect upper and lower wiring-line layers, a through hole is formed in a given location of the substrate. By making the circumference of the through hole using plating have conductivity, etc. or by filling the through hole with conductive paste, a multi-layered printed wiring board is formed.
In this method, however, pads on which components are mounted cannot be formed in the through hole portion, and the diameter of the through hole is generally about 0.3 mm. Accordingly, this method is difficult to be used for high-density mounting.
In light of this background, a method was disclosed in which a multi-layered printed wiring board for high-density mounting is manufactured using photosensitive resin without penetrating the substrate (see e.g., Japanese Unexamined Patent Application Publication No. 10-284841 and No. 10-200258). However, since this fabrication method includes a photolithography process or a screen printing process, the process becomes complicated. It is also difficult to form a minute pattern in which the ratio (L/S) of the line width to the space width is about 30 μm/30 μm.
In view of the above, a method has been proposed in which a wiring line or an insulating layer is formed using a droplet discharge method such as an inkjet method (see e.g., Japanese Unexamined Patent Application Publication No. 2003-309369 and No. 2003-318542).
The known techniques as described above, however, have the following problems.
If multi-layered wiring of a multi-layered printed wiring board, etc. is to be formed, a conductor post is needed to electrically connect the lower wiring line and the upper wiring line. As far as the conductor post is concerned, if the conductor post is formed by the droplet discharge method such as an inkjet method, the height of the conductor post obtained becomes unstable due to spreading by wetting. This makes it difficult to control the height of the conductor post. Accordingly, when a plurality of conductor posts is formed on the same surface, it is difficult to control the height of the conductor posts. Thus, there is a possibility that defective continuity may occur between the lower wiring line and the upper wiring line due to variations in height between the conductor posts.
Furthermore, a photolithography process using a mask is frequently used in order to form the conductor posts. There is also a problem in that the productivity is low.